This invention relates to a developer material coating apparatus for coating granular developer material on a support member such as a plain paper to form a developer sheet for a color image, and more particularly to a developer material coating apparatus in which the developer material is selectively coated on a desired portion of the support member.
To form a color image on a support member such as a plain paper, there has been known an image forming apparatus such as a color copying machine which utilizes microcapsules encapsulating dye precursor, photo-polymerization initiator, etc. and having a mechanical strength variable in accordance with intensity of light irradiated thereto. In this type of image forming apparatus, a microcapsule sheet on which the microcapsules are carried and to which light has been irradiated through an original is closely contacted with a developer sheet which is formed by coating granular developer material on the surface of a support member such as a plain paper or the like in a developer material coating apparatus, and these contacted sheets are fed to a pressure-developing unit to be subjected to a pressure development. In the pressure-developing unit, those microcapsules which have not been exposed to the light and thus have low mechanical strength are ruptured under pressure to issue the dye precursor therefrom, and the dye precursor issued from the microcapsules are reacted with the developer material on the developer sheet to form a visible image on the developer sheet. Thereafter, the developer sheet having the visible image thereon is fed to a heat-fixing unit to thermally fix the visible image on the developer sheet.
FIG. 1 shows a conventional developer material coating apparatus used in the image forming apparatus as described above.
The conventional developer material coating apparatus as shown in FIG. 1 includes a developer material coating unit, a support member feeding unit and a casing C having a sheet inlet 29 for inserting the support member therethrough and a sheet outlet 28 for discharging therethrough a developer sheet which is formed of the support member and the developer material layer coated on the support member. The developer material coating unit and the support member feeding unit are accommodated in the casing C.
The developer material coating unit comprises a tank (hopper) 20 for accommodating granular developer material S, a rotatable carry roller 22 for feeding the developer material to a developer material coating region 27 defined between the support member feeding unit and the developer material coating unit while carrying the developer material thereon, and a supply roller 21 provided beside the carry roller 22 for triboelectrically charging the developer material in cooperation with the carry roller 22 and supplying the charged developer material to the surface of the carry roller 22. As shown in FIG. 1, the carry roller 22 is grounded.
Further, the support member feeding unit comprises a counter electrode roller 23 disposed spacedly away from the carry roller 22 at a distance (d) so as to confront the carry roller 22, a pair of guide rollers 25a and 25b which are provided away from the counter electrode roller 23 and near to the sheet outlet 28 and the sheet inlet 29, respectively, a carry belt 24 such as an endless belt suspended among the counter electrode roller 23 and the guide rollers 25a and 25b for carrying the support member P thereon, and a D.C. voltage source 26 for applying a voltage to the counter electrode roller 23. In this case, if the developer material is positively charged in the developer material coating unit, a negative voltage is supplied to the counter electrode roller 23 through one terminal of the voltage source 26 to electrostatically attract the positively-charged developer material S to the counter electrode roller 23. The other terminal, that is, a positive terminal of the voltage source 26 is grounded as shown in FIG. 1. On the other hand, if the developer material is negatively charged, a positive voltage is supplied to the counter electrode roller 23.
An operation of producing a developer sheet from the support member such as a plain paper and the developer material will be described hereunder.
The carry roller 22 and the supply roller 21 are rotated while contacted with each other to thereby triboelectrically charge particles of the developer material S in the tank 20. A polarity of the charged developer material S is dependent on a physical property of the developer material, a kind of material constituting the surface of the carry roller, etc., and in this embodiment the developer material S is assumed to be positively charged. The positively-charged particles of the developer material S are attached to the peripheral surface of the carry roller 22 and are fed to the developer material coating region 27 by rotating the carry roller 22 by a motor (not shown). The counter electrode roller 23 is supplied with a negative voltage from the D.C. voltage source 26, and the carry belt 24 travels clockwisely by rotation of the counter electrode roller 23 and the guide rollers 25a and 25b. The support member P such as a plain paper is carried on the carry belt 24 and fed to the developer material coating region 27 through the feeding operation of the carry belt 24.
As described above, since the counter electrode roller 23 is kept at a negative potential and the carry roller 22 is grounded, an electric field occurs in the developer material coating region 27 defined between the counter electrode roller 23 and the carry roller 22. Accordingly, the positively-charged particles of the developer material S are electrostatically attracted (that is, flights) from the carry roller 22 toward the counter electrode roller 23, and are attached to the surface of the support member P to form a developer material layer m on the support member P.
The carry roller 22 used in the developer material coating apparatus 50 comprises a grounded metal shaft and a sleeve-type insulating member formed of epoxy resin or the like which surrounds the metal shaft. The developer material S is triboelectrically charged due to the friction between the developer material S and the surface of the insulating member of the carry roller 22. When the particles of the developer material S are positively charged, the surface of the insulating member of the carry roller 22 is charged at the opposite polarity to that of the developer material S (in this case, negatively), and the positively-charged particles of the developer material S are electrostatically attached to the surface of the insulating member of the carry roller 22.
In the conventional developer material coating apparatus thus constructed, the whole surface of the support member is coated with the developer material, that is, any portion on the surface of the support member is coated with the developer material. In a case where a user wants to print, by a laser printer or a typewriter, letters, characters and other images on a blank portion on the developer sheet on which a color image has not been formed in the image forming apparatus, however, it is liable to occur that the letters, characters and other images can not be printed even on the blank portion or are blurred even if printed on the blank portion, because the developer material is coated on the whole surface of the developing sheet and thus prevents the printing of the letters, characters and other images on any portion of the developing sheet.